Specific effects on human neutrophils of antibodies to a membrane protein constituent of neutrophil receptors for chemotactic formyl-methionyl peptides.

IgG and Fab were prepared from goat antisera to MP-2, the quantitatively predominant membrane protein constituent of human neutrophil receptors for chemotactic formyl-methionyl peptides. Only 10%–25% of the f-Met-Leu-Phe combining sites of MP-2 purified from neutrophil membranes that had been solubilized in Nonidet P40 exhibited binding constants similar in magnitude to those of the receptors in intact neutrophils, while the remainder of the sites retained a mean of 2% of the affinity of native receptors. Purified MP-2 elicited IgG antibodies predominantly to framework determinants, rather than the combining site, of the f-Met-Leu-Phe receptors. IgG antibodies, but not Fab, evoked the release of significant quantities of β-glucuronidase and lysozyme from neutrophils. Saturating concentrations of Fab bound to a mean of 65,000 determinants per neutrophil, as assessed with 125I-Fab, but failed to stimulate neutrophil chemotaxis or chemokinesis, and inhibited by 15% or less the binding of [3H]f-Met-Leu-Phe to intact neutrophils. Fab of anti-MP-2 inhibited neutrophil chemotactic responses to f-Met-Leu-Phe by up to 80%, without influencing the responses to equally chemotactic concentrations of fragments of C5 and of leukotriene B4. Preincubation of neutrophils for 2–30 min at 37° with concentrations of f-Met-Leu-Phe which suppressed significantly the number of receptors available to [3H]f-Met-Leu-Phe, increased the number of receptors detected by 125I-Fab of anti-MP-2, while neither fragments of C5 nor leukotriene B4 altered the number of receptors determined by either assay. Antibodies to non-combining site determinants of chemotactic peptide receptors provide a novel immunospecific probe for studies of the regulation of neutrophil chemotaxis.